Wolodymyr Czubatyj

Metal-Insulator-Semiconductor Solar Cells Using Amorphous Si:F:H Alloys

Amorphous hydrogenated silicon (a-Si:H) alloys produced from the radio-frequency glow discharge of SiH4 gas have been studied extensively in recent years(1). Thin-film photovoltaic devices have been fabricated from these alloys in Schottky barrier2 metal-insulator-semiconductor (MIS),3 and p-i-n 4 configurations with conversion efficiencies of up to 5.5, 4.8, and 4.5%, respectively.*

On the mechanism of light‐induced effects in hydrogenated amorphous silicon alloys

We have investigated the effects of both forward bias current soaking in the dark and prolonged light exposure on the photovoltaic properties of lightly doped, n‐ and p‐type hydrogenated amorphous silicon Schottky barrier diodes. The results show that recombination rather than single carrier trapping is responsible for the light‐induced changes.

Minority‐carrier diffusion lengths in amorphous silicon‐based alloys

In this paper, we present results of collection efficiency versus wavelength measurements on thick (⩾1 μm) amorphous silicon Schottky barrier photovoltaic devices illuminated through both the ohmic and Schottky contacts. These results enable us to infer the zero‐field minority carrier diffusion length in amorphous silicon‐based alloys by using an appropriate theoretical model. For intrinsic a‐Si:H (hydrogen) films produced by the glow discharge of silane this was found to be ∼2,100 A. Our novel approach of illuminating the devices through the ohmic contact ensures that the collection efficiency results are extremely sensitive to the minority carrier diffusion length, and we also compare this approach to surface photovoltage type experiments which we show can lead to overestimation of this quantity.

Observation of two modes of current transport through phosphorus‐doped amorphous hydrogenated silicon Schottky barriers

The influence of phosphorus impurities in the active layer of amorphous hydrogenated silicon Schottky barriers is investigated by experimentally studying the current‐voltage characteristics of the structure and the physical and electronic properties of the material. With increasing phosphorus concentration excess diode currents develop. Numerical analysis shows that (1) these currents are due to hopping within an impurity band produced by the impurities and (2) a two‐channel conduction mechanism is in quantitative agreement with the data.

Low-temperature polycrystalline-silicon TFT on 7059 glass

A polycrystalline-silicon (poly-Si) thin-film transistor (TFT) deposited at low temperature on Corning 7059 glass is reported. It has practical applications for low-cost thin-film display and imaging electronics manufacturing. All the process steps used to fabricate the poly-Si device take place at temperatures of 550 degrees C or less. The poly-Si films exhibit crystallite grain sizes on the order of 5000 AA, and the fabricated devices show field-effect mobilities of 10-20 cm/sup 2//V-s and threshold voltages around zero. A plasma process to form the source and drain contacts has also been developed.<<ETX>>

Schottky barrier profiles in amorphous silicon-based materials

Abstract The localized state density for a-Si:H and a-Si:H:F can be reasonably approximated by a hyperbolic function. Solution of Poissons equation leads to potential profiles in the depletion region. The predicted width of the depletion region is in reasonable agreement with the results obtained from C-V experiments.

Double‐injection field‐effect transistor: A new type of solid‐state device

We propose a new general principle of operation for solid‐state devices, and demonstrate a novel transistor which we call a double‐injection field‐effect transistor, based on this principle. We have fabricated amorphous silicon alloy double‐injection transistors operating on the modulation of a double‐injection current by a gate field covering the complete path of the current channel. Using these amorphous silicon alloy double‐injection transistors, we have achieved currents over 20 times those theoretically possible for conventional amorphous silicon field‐effect transistors operating under similar conditions. This new principle, applicable to both thin‐film amorphous and crystalline devices, offers the potential of high‐current, high‐speed field‐effect transistors with modulated optical emission.

Differences between the bonding of oxygen in glow discharge deposited a-Si:H and a-Ge:H

Abstract We have prepared a-Si:(H,O) and a-Ge:(H,O) films by the glow discharge technique and have studied the bonding of oxygen by IR absorption spectroscopy. We find qualitatively different behavior in these two alloy systems, which we relate to differences in plasma phase interactions in which precursor molecular groups are formed.

Some electrical and optical properties of a-Si:F:H alloys

Amorphous Si:F:H with desirable properties for photovoltaic applications can be fabricated by the glow discharge of SiF4 and H2. The preparation conditions influence the properties of the resultant alloy. For instance, altering the ratio of SiF4 to H2 from 80 to 5 can alter the localized state density from 1019cm−3eV−1 to ≃ 1016cm−3eV-1, respectively. The conduction mechanisms are altered and there are vast changes in the photoconductivity as the density of recombination centers is decreased. The lower density of states achieved in the a-Si:F:H alloy reflects in the ease of doping. In addition, the lower density of states in a-Si:F:H alloy should result in a wider depletion region than reported for the a-Si:H alloy when fabricated within the device configuration. Results of C-V measurements using Au Schottky barrier devices confirm this.

New developments in optical phase-change memory

Phase change technology has progressed from the original invention of Ovshinsky to become the leading choice for rewritable optical disks. ECDs early work in phase change materials and methods for operating in a direct overwrite fashion were crucial to the successes that have been achieved. Since the introduction of the first rewritable phase change products in 1991, the market has expanded from CD-RW into rewritable DVD with creative work going on worldwide. Phase change technology is ideally suited to address the continuous demand for increased storage capacity. First, laser beams can be focused to ever-smaller spot sizes using shorter wavelength lasers and higher performance optics. Blue lasers are now commercially viable and high numerical aperture and near field lenses have been demonstrated. Second, multilevel approaches can be used to increase capacity by a factor of three or more with concomitant increases in data transfer rate. In addition, ECD has decreased manufacturing costs through the use of innovative production technology. These factors combine to accelerate the widespread use of phase change technology. As in all our technologies, such as thin film photovoltaics, nickel metal hydride batteries, hydrogen storage systems, fuel cells, electrical memory, etc., we have invented the materials, the products, the production machines and the production processes for high rate, low-cost manufacture.